A liquid chromatograph uses a separation column for separating a sample to be analyzed, and a reaction column for mixing a reagent with the sample to cause reaction in the case of amino acid analysis. When a packing material to be packed in the column has a bead-shape, filters are provided at both ends of the column for the purpose of enclosing the packing material within the column. A mesh size of the filter is set to be smaller than a particle diameter of the packing material in the form of a bead.
As a material of the filter, there has been conventionally used stainless steel including iron Fe as a main component, and chrome Cr, manganese Mn, nickel Ni and molybdenum Mo. Depending on the kind of the stainless steel, niobium Nb, and aluminum Al may be included in addition to chrome Cr, manganese Mn, nickel Ni and molybdenum Mo. The stainless steel includes nickel Ni of about 10 to 14%, and iron Fe of about 70% as the main component.
Amino acids, amino acid analogues and proteins composed by those amino acids have a property of adsorbing on a surface of a stainless steel material. Therefore, when analyzing chemical species such as amino acids and proteins by a liquid chromatograph apparatus using a stainless steel material for a flow channel, the chemical species adsorbs on the surface of the flow channel, and therefore may cause an adverse effect on analysis results.
In particular, it is known that peptides and proteins including cystine which is a kind of amino acid show a strong interaction with iron ions. According to Non Patent Literature 1, disulfide having two sulfur atoms specifically adsorbs on an iron atom on a metallic surface, and temporarily forms iron mercaptide. Ultimately, C—S bond is cut, and the surface of the stainless steel material is covered in a state of iron sulfide. This phenomenon is called a disulfide adsorption phenomenon.
Further, in the case that the filter used for the column of the liquid chromatograph is made from a stainless steel material, a peptide containing cystine adsorbs on a surface of the stainless steel material, and therefore may cause a tailing phenomenon in which a peak obtained in a chromatogram which is an analysis result splays out.
Furthermore, in the case that adsorption of a peptide onto the filter is extreme, most of the peptide is not eluted from the column, which causes the problem that a sample recovery rate is lowered.